This project has four goals. The first is to determine which invertebrates are of major economic or medical importance on the Crow and Northern Cheyenne Indian Reservations. While the invertebrates of agricultural importance are fairly well known those of medical or veterinary importance are poorly understood. This part of the project will involve literature searches, interviews and compiling of Montana State University (MSU) Extension records. The second goal is to develop field scouting programs and economic thresholds for the Russian wheat aphid -- an important new wheat and barley pest in Southwestern Montana. This part of the project will involve extensive field surveys using methods developed by MSU and other Western universities. The third goal is to determine the species and populations of mosquitoes. Though mosquitoes are common on both Reservations little is known about the species present, their population densities, and their medical and veterinary impact. This part of the project will involve field surveys of adult and larval populations. The final project goal is to determine the common species of Lymnaeid snails on both Reservations and their biological characteristics. In addition, the snails will be for cattle liver flukes and the disease commonly known as "swimmers' itch". Virtually nothing is known about snails and their secondary host relationships in Western Montana. This project will contribute to a better understanding of the biomedical and economic importance of invertebrates in two of Montana's neighboring Indian reservations.